I was referring to the actual single 1.8GHz PowerMac. This one has a very different logic board design (smaller, slower and stripped down, compared to the dual), and the CPU is soldered on it, just like the iMacs.

The older single 1.8GHz and 1.6GHz PowerMacs have infact their CPU un a separate card, like on your pics. They mainly had the same logic board than the duals, just with a few less components.